In certain integrated circuit layouts, a multitude of monolithic semiconductor devices are mounted on an insulative substrate with an electrical interconnection network that interconnects the semiconductor circuit chips. The chips are mounted at chip sites on the substrate by solder columns that join terminals of the chips to the interconnection network.
One technique for forming these solder columns involves fusing solder balls at each of the chip terminals to pads on the substrate with a solder reflow technique. This technique is described in U.S. Pat. No. 3,429,040, and in the article "A Critique of Chip Joinings Techniques" by L. F. Miller, beginning on page 50 of the April, 1970 issue of Solid State Technology.
With a large number of semiconductor chips on a substrate, it becomes necessary from time to time to remove a defective chip from the substrate and replace it with an operating chip. One technique for removing the defective chip is to repeatedly twist the chip relative to the substrate until the solder columns rupture. This removal technique has a number of problems. One of them is that it leaves a residue from the solder columns at the chip site which must be removed before a new chip can be attached to the substrate at that site. Another problem with the technique is that it sometimes results in damage to the interconnection network on the substrate.
One method for removing the residue of the solder columns from the chip site can be found in U.S. Application Ser. No. 036,912 which was filed May 7, 1979, and now abandoned and is entitled "Apparatus and Method for Rework Dressing of Chip Site". In this method, a mask is placed over the chip site. This mask has holes in it that expose the remnants of the solder columns while shielding the remainder of the chip site. A brush is then used to remove the excess solder of the remnants.
A difficulty with this chip site dressing method, is that in order for it to work satisfactorily, the residue solder columns must be substantially perpendicular to fit through the openings in the mask. If they are bent one direction during the removal of the chip, which frequently happens with the described chip removal technique, the mask will not fit over the residue of the solder columns and the dressing technique cannot be employed. Furthermore, the dressing method does not compensate for the removal of too much solder from the chip site by the chip removal technique.
The use of embrittlement caused by cooling to strip insulation off is described in U.S. Pat. No. 3,936,922 and U.S. Pat. No. 3,556,366, describes the use of thermal shock to fracture semiconductor substrates.